There has been widely used a semiconductor optical integrated circuit including a semiconductor layer in which an optical circuit is provided. For example, Patent Literature 1 discloses a semiconductor optical integrated circuit including a semiconductor layer in which an optical modulator, which utilizes a thermooptic effect, is provided.
FIG. 6 illustrates a configuration of a semiconductor optical integrated circuit 6 disclosed in Patent Literature 1. The semiconductor optical integrated circuit 6 includes (i) a substrate 61 made of silicon, (ii) a lower cladding layer 62 made of silica, (iii) a semiconductor layer 63 made of silicon, and (iv) an upper cladding layer 64 made of silica. The semiconductor layer 63 includes an optical waveguide LG and heater parts H0 and H1.
According to the semiconductor optical integrated circuit 6, a voltage is applied across the heater parts H0 and H1. This causes the heater parts H0 and H1 to generate heats. It is therefore possible to modulate a phase of light which propagates the optical waveguide LG. This is because a refractive index of the optical waveguide LG changes due to a thermooptic effect which is brought about by an increase in temperature of the optical waveguide LG due to the heats generated by the heater parts H0 and H1.